Determining the level of fatigue of a user may be useful in many situations. For example, some activities require a great degree of concentration. It is useful to be able to provide to the user carrying out such activity or a third party an indication of the level of fatigue of the user. Indeed, it has been observed that a change in behavior upon carry out an activity may lead to very different results in terms of achievement of the activity. Typically, when a person is driving it can be very useful to analyze the fatigue level of the person so as to provide an alert when the determined fatigue level is greater than a threshold value and driving represents a risk. Therefore, there is a need for a device and a method for determining accurately the fatigue level of a person. One object of the present invention is to provide such a device and method providing such determination.